U.S. Pat. No. 8,864,552 discloses such a machine for grinding a cam having an outer surface with outwardly convex and outwardly concave portions. The machine has a frame and means on the frame for holding the cam and rotating it about a main axis. A pair of drive motors have respective output axes generally diametrally flanking the main axis and are carried on respective carriages shiftable on the frame radially of the main axis. One of the motors is shiftable into an inner position in which the main axis extends through the one drive motor. Respective grinding wheels are rotatable by the motors about the respective axes. The wheel of the one motor is of substantially smaller diameter than the wheel of the other motor and also of smaller diameter than the one motor. In addition the grinding wheels are, relative to the main axis, axially between the drive motors.